In modern semiconductor technology, metal silicides, which are generally formed from reactions between metals and silicon, are often used in various semiconductor devices. For example, metal silicides are usually incorporated in transistors to provide low resistance at their gate, source and drain. In particular, with the development of semiconductor technology, semiconductor devices tend to be increasingly integrated and miniaturized, allowing increased ease of use of metal silicides resulting from self-aligned silicide (salicide) processes in the fabrication of semiconductor devices.
FIGS. 1a and 1b schematically illustrate a conventional process for forming a metal silicide layer. This process, for example includes:
providing a substrate 10 which may be a silicon substrate, as shown in FIG. 1a; 
depositing a metal layer 20 over the substrate 10, also as shown in FIG. 1a; and
performing a thermal annealing process, as shown in FIG. 1b, so that metal (M) atoms diffuse from the metal layer 20 into the substrate 10 and react with silicon (Si) therein to form a metal silicide (MSix), which constitutes the metal silicide layer 30.
As shown in FIG. 1b, in the above conventional method, the resulting metal silicide layer 30 may extend a relatively great depth into the substrate 10, rendering a great consumption of the substrate 10. Moreover, based on an in-depth analysis of the metal silicide layer, the inventors of the present application have found that agglomeration of the metal silicide (MSix) tend to occur in the metal silicide layer, which will lead to a number of pinhole defects within the substrate as well as rough surfaces of the metal silicide layer 30, i.e., a rough top surface and a rough interface with the substrate 10.